The Truth About Wireless Charging

Inductive charging (also known as wireless charging or cordless charging) uses an electromagnetic field to transfer energy between two objects through electromagnetic induction. This is usually done with a charging station. Energy is sent through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device.

Induction chargers use an induction coil to create an alternating electromagnetic field from within a charging base, and a second induction coil in the portable device takes power from the electromagnetic field and converts it back into electric current to charge the battery. The two induction coils in proximity combine to form an electrical transformer. Greater distances between sender and receiver coils can be achieved when the inductive charging system uses a resonant inductive coupling.

Recent improvements to this resonant system include using a movable transmission coil (i.e. mounted on an elevating platform or arm) and the use of other materials for the receiver coil made of silver-plated copper or sometimes aluminum to minimize weight and decrease resistance due to the skin effect.

Advantages

Protected connections – No corrosion when the electronics are all enclosed, away from water or oxygen in the atmosphere. Less risk of electrical faults such as short circuit due to insulation failure, especially where connections are made or broken frequently.

Low infection risk – For embedded medical devices, transmission of power via a magnetic field passing through the skin avoids the infection risks associated with wires penetrating the skin.

Durability – Without the need to constantly plug and unplug the device, there is significantly less wear and tear on the socket of the device and the attaching cable.

Increased convenience and aesthetic quality – No need for cables.

Automated high power inductive charging of electric vehicles allows for more frequent charging events and consequential driving range extension.

Inductive charging systems can be operated automatically without dependence on people to plug and unplug. This results in higher reliability.

Inductive charging of electric vehicles at high power levels enables charging of electric vehicles while in motion (also known as dynamic charging).

Disadvantages

Slower charging – Due to the lower efficiency, devices take longer to charge when supplied power is the same amount.

More expensive – Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing.

Inconvenience – When a mobile device is connected to a cable, it can be moved around (albeit in a limited range) and operated while charging. In most implementations of inductive charging, the mobile device must be left on a pad to charge, and thus can’t be moved around or easily operated while charging. With some standards, charging can be maintained at a distance, but only with nothing present in between the transmitter and receiver.

Compatible standards – Not all devices are compatible with different inductive chargers. However, some devices have started to support multiple standards.

Inefficiency – Inductive charging is not as efficient as direct charging. In one application, the phone being charged gets hot. Continued exposure to heat can result in battery damage.

Cords – One major advantage is that devices can be charged without cords, but this is not entirely true. There is no direct connection to the device being charged; however, cords are required to provide power to the transmitter.

Newer approaches reduce transfer losses through the use of ultra thin coils, higher frequencies, and optimized drive electronics. This results in more efficient and compact chargers and receivers, facilitating their integration into mobile devices or batteries with minimal changes required. These technologies provide charging times comparable to wired approaches, and they are rapidly finding their way into mobile devices.

For example, the Magne Charge vehicle recharger system employs high-frequency induction to deliver high power at an efficiency of 86% (6.6 kW power delivery from a 7.68 kW power draw).

In July 2009 the researchers successfully supplied up to 60% power to a bus over a gap of 12 centimeters (4.7 in).

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed an electric transport system (called Online Electric Vehicle, OLEV) where the vehicles draw power from cables underneath the surface of the road via non-contact magnetic charging (where a power source is placed underneath the road surface and power is wirelessly picked up on the vehicle itself). As a possible solution to traffic congestion and to improve overall efficiency by minimizing air resistance and so reduce energy consumption, the test vehicles followed the power track in a convoy formation.

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